Soil/metal supporting structures are most commonly in the form of culverts which are either circumferentially continuous or have an open bottom commonly referred to as either a box culvert or a re-entrant arch shaped culvert. These culverts are used to direct water ways and for use as bridges in roadways, railways and the like. The design of the soil/metal supporting culvert is to accommodate designed soil loads and as well anticipated rolling loads and static loads which might be applied to the roadway, railway and the like. Usually such structures are formed from steel or aluminum. As is usually the case the plates used in forming the support structure are corrugated in the direction of their longitudinal length. The extent of corrugation depends upon the thickness and radius of curvature in the panel.
Culverts in the form of elliptical, round, pear, arch or pipe-arch shapes or the box culvert shape include portions across their section which are curved and have a relatively short radius of curvature. Such short radius of curvature is usually in the range of 750 mm to 2,500 mm in the longitudinal direction of the panel. For example, such short radius regions in the box culvert structure is described in respect of applicant's co-pending U.S. patent application Ser. No. 08/026,860 filed Mar. 5, 1993. That application in particular relates a form of continuous reinforcement in an uninterrupted manner to provide an optimum load carrying capacity for a selected extent of reinforcement. Although the short radius of curvature panels for this box culvert can be formed using existing types of roll forming and bending presses, the equipment is expensive and complex to use in order to achieve the manufacture of short radius panels having consistent dimensional configurations so that the panels can be readily attached to one another by way of appropriate alignment with one another so that bolts may be used to fasten the panels together through the aligned bolt holes. The same approach applies with respect to other culvert styles involving short radius of curvature sections. It is generally understood that even with the rather expensive approach to cold forming such radius of curvature panels, some distortion can occur due to the short radius which can hamper erection of the structure and hence, delay field insulation.
Another problem to be considered in the cold forming of these thick gauge panels to the short radius specifications is that cold working normally decreases ductility of the panels. Such decrease in ductility can be such that the structure can no longer be designed on the basis of plastic analysis and instead must be designed on the basis of elastic analysis which requires the use of even thicker gauge materials with considerably more reinforcing. It therefore becomes very important that in such cold working of the panels to provide the specified short radius, the bending be carried out in a manner which does not reduce the ductility, induce case hardening in the outside of the structure and also avoids the possibility of forming micro-cracks in the outside portions of the structure. Such problems are addressed in U.S. Pat. No. 5,118,218. It is suggested that when forming short radius of curvature panel sections, that such forming be done while the panels are hot to avoid any case hardening problems. It is also suggested that aluminum sheet material be used in place of steel since it is more easily bent. However, as described, aluminum has less ductility than steel when it comes to plastic design analysis for the soil/metal structure. There continues to be a problem in respect of cold forming short radius of curvature panel sections particularly with deep corrugations in the range of 50 to 200 mm.
Other than the suggested hot forming of the short radius of curvature for the deep corrugation panels, there does not appear to be much other guidance in the prior art in respect of how such deep corrugation panels of thick gauge may be bent to short radius specifications without inducing case hardening, embrittlement and micro-cracks.
There are a number of examples in the bending of light gauge deep corrugated panels for use in arch shaped building structures. These structures are designed to carry a snow load but not a soil load such as required in bridges or the like so that the light gauge material is quite acceptable. These arch type buildings more commonly referred to as quonset huts are constructed with cold formed panels using either trapezoidal or sinusoidal corrugation profiles with depths up to 200 mm and radius of curvature from 3000 to 12,000 mm. The light guage material used in forming these panels is in the range of 0.75 mm to 1.5 mm. With such thin gauged materials and large radius of curvature there is very little working of the metal in cold forming panels for use in such structures to the desired radius of curvature. However, to facilitate such bending, it is well known that some form of cross-deformation is employed on the inside ridge of these panels to facilitate bending. Such cross-deformation may be in the form of metal tucks, diamond shaped indents and sinusoidal shaped indents and the like. Such corrugations which in essence extend transversely of the longitudinal direction of panel facilitate bending of the light gauge material to the specified radius of curvature. By virtue of the thin gauge material, it is generally thought that there is very little if any cold working of the material so that there is very little if any loss in ductility. Loss in ductility however is not of great concern in the design of arch shaped buildings because they are designed on an elastic basis taking into consideration snow loads and wind resistance. Furthermore, with this type of arch building the depth of the cross corrugations in the curved panel is usually from only 1.5 to 3 mm with a pitch of 25 to 50 mm which again contributes to the general understanding that there is little if any cold working of the material in forming the desired radius of curvature in the panel. In any event, the use of cross corrugations in this light gauge material for arch structures does assist in the cold forming of the structure by avoiding stretching of the outside surface and by virtue of the cross corrugation, shortening the inside arc length of the panel to achieve the desired radius. Furthermore, such corrugations can be of a variety of shapes which are in line, discontinuous or misaligned where there depth usually reduces to zero as the cross corrugation approaches the apex of the outside ridge of the corrugated panel.
There have of course been various attempts to improve on the overall structural benefits in the panel designs for arch buildings and their types of interconnections. For example, as disclosed in U.S. Pat. No. 3,959,942, a specifically designed spacer and transverse reinforcing beam is provided for interconnecting of panels preferably along a single axis for the entire length of the structure. Such interconnection may be acceptable for light gauge materials where the only consideration is snow loading. U.S. Pat. No. 3,968,603 also discusses the use of cross-corrugations in the base of the trough section of the longitudinally extended corrugated panels. It is recognized however that there is a problem in bending corrugated structures having longitudinal corrugations in the range of 120 mm up to 250 mm. With such light gauge material in the suggested range of 16 to 22 gauge, which in millimeters is approximately 1.5 mm in thickness or less, an approach in providing sections of smaller depth which are interconnected in the web region are provided. The smaller depth corrugations facilitate bending of the panels to arch building structure radii without having to form cross-corrugations therein.
Outside of the existing techniques for roll forming and pressing short radius in deep corrugated panels of thick gauge, there does not appear to any other more economical approach. This is particularly the situation considering the general understanding that cold working of the thicker gauge panels to short radius specifications can significantly decrease ductility, embrittle the resulting structure and perhaps even induce the formation of micro-cracks in the outer ridges in the panel.